Photoelectric device



Nov. 5, 1940.

A. M L. NICOLSON I PHOTOELECTRIC DEVICE Original Fil u y '7, 1930 3 HMPI. lflf/E INVENTOR #xaflder /l/ 16022 Mcolsalz BY W 7 y W ATTORN Y5 Patented Nov. 5, 1940 PATENT OFFICE IPHOTOELECTRIC DEVICE Alexander McLean Nicolson, New York, N. Y., as-

signor to Communication Patents, Inc., New York, N. Y., acorporation of Delaware Original application July 7, 1930, Serial No. 466,079. Divided and this. application January 29, 1938, Serial No. 187,758

. 3 Claims.

This invention relates to improvements in photo-sensitive devices ofthe class whose elements include an anode, a cooperating lightsensitive cathode, and the interconnections therefor. More specifically the invention relates to photoelectric tube arrangements of the type used in television systems, such, as, for example, the system disclosed in my copending application filed July 7, 1930, Serial No. 466,079, now Patent No. 2, 108,827, dated February 22, 1938, of which the present application is a division, although the invention is not limited to that use.

In the system disclosed in said copending application, the image of a distant or near scene is focused upon the cathode of a photoelectric tube having a non-linear characteristic. The focusing of the image on the cathode causes a steady total emission of electrons to the anode of the tube, and produces asteady electric current in the input circuit of the photoelectric current amplifier. A scanning ray of light, produced in any well known manner, but preferably in the form of an. electrodynamic are along electrode rails in a magnetic field, i. e., an actinic ray, is employed for scanning the image on the cathode. Since the intensity of the light of the scanning ray is substantially constant, variations in the current output of the tube areobtained through the non-linear characteristic of the photoelectric tube. Thus, when the scanning ray is shifted from a dark area of the scene to a lighter area, the current output of the tube will be greater. This variation in current in accordance with the variations in light and dark areas of the scanned image will reproduce the image at a receiving station. The definition of all areas of the reproduced image at the receiving station is greatly enhanced, as well as the efficiency and rapidity of response of the system, by the use of the photoelectric tube arrangement of the present invention.

In accordance with the presentinvention, a photoelectric tube arrangement having a. nonlinear characteristic is provided, in which the cathode is translucent andwill transmit light through it as well as being able to hold the image of a scene projected thereon, intercepting sufiicient light for that purpose, The cathode is sensitized on its opposite surfaces for response to the character of the light to be projected thereon, one surface being adapted to be responsive to the spectrum light of the image projected thereon, and the opposite surface beingadapted to be I responsive to thescanning ray, which preferably is actinic, the. cathode being translucent. to. both optical functions. An anode is positioned adjacent each surface of the cathode and the anodes are so constructed as not to materially intercept the projection of the image light or the scanning light on the corresponding surfaces of the oathode. Since the distance between the source of the scanning ray and the cathode is short because of space requirements, the cathode and the complementary anodes are preferably curved about the source of the scanning ray, so that the scanning is uniform over every unit of area of the cathode and blurring of the image at its borders, due to irregular scanning, as is common with fiat cathodes, is avoided. The output circuits of the tubes are preferably arranged with a regenerative feed back coupling for increased efficiency. Details of construction and further advantages of the photoelectric tube arrangement of this invention will become apparent upon examination of the accompanying drawing, which is a crosssection of the tube and scanning arrangement with a diagram of the external electrical circuits.

Referring to the drawing, numeral l9 designates acamera casing divided into two chambers H and 12 by a partition 53. Chamber ll contains a specially designed photoelectric tube I4 supported on a suitable base l5 and locked thereon in vertically adjusted position by thumb-screw IS. The chamber I2 contains an electrodynamic arc screen ll supported on a suitable base IS in which it is locked in vertically adjusted position by thumb-screw IS. The screen I1 is positioned in alignment with tube It and a focusing lens combination 20in the partition l3 directs the scanning ray from the screen H on the tube M. A focusing lens combination 2| in the opposite wall of the chamber ll directs the image 0, such as the scene to be transmitted, upon the tube M.

The tube I4 comprises an evacuated or gasfilled transparent envelope or tube 22 containing a cathode 23 and symmetrically arranged anodes '24 and 25 positioned on opposite sides of the cathode 23. The cathode '23 has a spherical curvature about the focus of the camera lens combination 2!! and the anodes 24 and 25 and the opposite surfaces of the envelope 22 are complementarily curved as shown. The advantage of the curved cathode 23 is that the projection path of the ray of light from the scanning screen I! is always a constant distance from the cathode Y23 and the image thereon. In this manner the intensityof the normal light is maintained constant at the image, so that a small and compact camera may be provided without distortion of the image and out-of-focus blurring at the borders,

as is commonly'the case with fiat cathode tubes. The screen I! thus may be fixed relatively to the cathode 23 for scanning all sorts of images.

The cathode 23 of the tube I4 is translucent and will transmit light through it as well as being able to hold the image of the scene projected thereon, intercepting sufficient light for that purpose. The opposite surfaces of the cathode 23 are provided orcoated with active light-sensitive material, such as potassium or the like, well .known in the art, the material on each cathode surface being responsive to the character of the light projected thereon, and being continuous, i. e., substantially uniformly conductive as compared to individual, insulated photosensitive tube. The anodes 24 and 25 are so constructed, such as of fine wire as shown, as not to materially intercept the light directed on the opposite surfaces of the cathode, the light from the object 0 being projected on the left hand side of the cathode 23, while the scanning ray of the screen I! is projected on the right hand side of the cathode, as seen in the drawing. The double anode arrangement with the translucent cathode provides ,a very efficient tube, as well as an advantageous arrangement from the mechanical point of view.

The screen I! produces a strong scanning ray of substantially constant intensity in any welllmown manner, but preferably the ray is produced in the form of an electrodynamic arc along electrode rails 25 in a magnetic field producing actinic light as compared to the spectrum light reflected from the object 0. Scanning systems of this nature are shown in greater detail in my Patents Nos. 1,839,696 and 1,863,278. As shown in the drawing a field winding 21, in series with the electrode rails 25, is provided for producing the magnetic field. This winding 2'! is enclosed in a jacket 28 packed with suitable heat dissipating material 29,.such as steel wool or the like, and containing. a, passage 30 through which a suitable heat-conducting fluid is circulated to maintain the screen electrode rails 26 at a constant temperature .as well as for cooling the field winding 21.

The external electrical circuits include a photoelectric tube amplifier having either two tubes, or a single tube 3! with a double anode, as shown. For example, the grid 32 is connected to the cathode 23 of the photoelectric tube 14, while one anode 2 3 of the tube i4 is connected through a variable inductance 33 to an anode 34 of the amplifier tube 31. Similarly, the other anode 25 0f the tube I4 is connected through a variable inductance 35 to the anode 36 of the amplifier tube 3|. A variable resistance 31 is connected between the grid 32 and the filament of the tube 3! for controlling the operation of the tube I4, and the tube St. A plate potential 38 for the amplifier tube 3i, supplies also the operating voltage for photoelectric tube l4 through the primary of the output transformer 39, choke coils 40 and M, in parallel, the variable inductances 33 and 35 in parallel, tube anodes 24 and 25 in parallel, cathode 23, and grid 32.

An increase in electron emission of the cathode 2-3 to either of the anodes 24 or 25 of the tube will produce an increase in the voltage of the input circuit of the amplifier tube 3!, which will be transmitted through the output transformer 39 to a suitable amplifier 42. This output circuit has a tuning inductance 43 connected. therein which is employed for feed-back purposes and, with inductances 33 and 35, may be used to produce a certain amount of regeneration. The tube I4 accordingly is alternating current operated.

The scanning electrode rails 26 and field coil 21 are supplied from a suitable scanning generator 44 through conductors 45. The output of the amplifier 42 is also connected to conductors 45, for the purpose of increasing the intensity of the scanning ray producing are as the photoelectric tube l4 output currents are increased. This action will produce regeneration by increasing the intensity of the scanning ray in proportion to the increase in photoelectric tube current. That is, should the tube output current be considerably increased by the scanning ray falling 'on a highly illuminated area of the cathode 23, this increase will be augmented by the substantially simultaneous increase in the scanning ray intensity. When the ray falls on a less illuminated area, the contrast will thus be much greater than with the normal scanning ray.

The photoelectric tube l4 output currents and the arc producing currents are segregated by a filter 46 in the output circuit of the system. The output terminals 41 may be connected to suitable transmission apparatus 48. The impulses from the scanning generator 44 are transmitted along with the photoelectric tube l4 output currents for synchronizing the remote receiving screen with the transmitter 48. With the scanning generator 44 a direct current source, it is unnecessary to employ a filter.

The photoelectric tube arrangement of this invention is particularly adaptable to the television system described in the aforementioned copending parent application. In such a system, the tube [4 is preferably disposed between the scene 0 being televised and the scanning ray source ll. Since the cathode 23 is translucent, light reflected from the scene 0 impinges on both sensitized surfaces, and light from the scanning source I"! also impinges on both sensitized surfaces, so thatthe efiiciency of conversion from radiant to electrical energy is much higher in this photoelectric tube than in other photoelectric tubes used heretofore for this purpose.

It is evident that the efficiency of this novel photoelectric tubearrangement may be still further increased by coating'each side of the cathode with photo-sensitive material which is most sensitive to the luminous radiation falling on it. For example, in the above described television scanning system where visible light is focused on one side of the cathode and a scanning beam of ac-' tinic radiation is focused on the other side of the cathode, the side of the cathode nearest the scene may be coated with photo-sensitive material which is responsive to light from the sun or any i artificial lighting system, and the side nearest the scanning source may be coated with material especially sensitive to actinic radiation.

Obviously, the use of a photoelectric tube with a translucent'cathode is not limited to the television art, but is capable of adaptation to many other fields in which ,the transmission of light, either visible or invisible, through the cathode of a photoelectric tube may be desirable. Furthermore, this novel photoelectric tube is capable of modification in form and detail, and is not to be limited in any way by the embodiment described in the specification except as defined in the appended claims.

I claim:

1.'A photoelectric device, comprising a. transparent envelope, a translucent cathode in and spaced from said envelope and having electron- 76 emissive surfaces on opposite sides thereof to be activated by selected radiations, said cathode being pervious to said selected radiations, anodes at opposite sides of and in cooperative electronic relation to said cathode within said envelope, said anodes being pervious to said radiations so as not to materially intercept the radiations directed on said cathode.

2. A photoelectric device, comprising a transparent envelope, a translucent cathode therein having an electron-emissive surface to be activated by selected radiations and curved about a selected point external of said envelope, an anode in said envelope positioned in cooperative electronic relation to said surface, said anode being pervious to said radiations soas not tomaterially intercept the radiations directed on said cathode.

3. A photoelectric device comprising an envelope having a transparent Wall, a translucent cathode therein having an electron-emissive surface to be activated by selective radiations; said wall and said electron-emissive surface being complementarily spherically curved, said surface having a focal point which is spaced from said wall, and an anode positioned in cooperative electronic relation to said surface.

ALEXANDER McLEAN NICOLSON. 

